1. Field of the Invention
The present invention relates to toner, a development agent, and an image forming method,
2. Description of the Background
Electric or magnetic latent images are rendered visible with toner in an image forming apparatus employing electrophotography, an electrostatic recording device, etc.
For example, in electrophotography, an electrostatic image (latent image) is formed on an image bearing member (e.g., photoreceptor) and then developed with toner to form a toner image. The toner image is then transferred onto a recording medium such as paper and fixed thereon.
In an image forming apparatus employing a fixing system by heating, a great amount of electric power is required to fix the toner on the recording media such as paper by heating and fusing. Therefore, in terms of energy saving, the ability to fix the image at low temperature (hereinafter referred to as low temperature fixing property) is one of the key characteristics for the toner.
To obtain toner having a good low temperature fixing property, controlling the thermal characteristics of binder resins occupying a large part of the toner composition is necessary. For example, the low temperature fixing property tends to be improved by reducing the molecular weight of the binder resin and the glass transition temperature (Tg). However, this reduction creates another problem, that of lowering the upper limit of the fixing temperature, resulting in a narrow fixing range.
In general, there is a trade-off between fixing temperature and fixing range: the lower the fixing temperature, the narrower the fixing range. Therefore, much research has been directed to finding a good combination of fixing temperature and fixing range. For example, toner has been developed that includes both a binder resin having a low molecular weight component with a good low temperature fixing property and a polymer component produced by reaction of a copolymer (referred to as a prepolymer) having an isocyanate group and a polyamine to raise the upper limit of the fixing temperature.
Accordingly, to a certain degree the above-described toner achieves a good combination of the low temperature fixing property and a wide fixing range, but in the current climate of energy efficiency remains inadequate, due to its high-level demand for energy. In addition, the polymer component produced by such reaction is easily positively charged. Therefore, if this toner is used as a negatively charged toner, which is currently the main type of the toner in use, the toner cannot be sufficiently negatively charged.